The present invention relates to an iron type golf club head having a head impact face portion whose structure is improved and, more particularly, to an iron type golf club head wherein the impact face portion of a head body is constituted by a thin plate consisting of a thermoelastic type martensite transformation alloy so as to improve directional stability upon impact and increase a carry.
Conventional golf club heads having various structures have been proposed. For example, Japanese Patent Laid-Open (Kokai) No. 59-228874 discloses a wood type club head having a solid or hollow structure and constituted by a wood material such as persimmon, a metal material such as stainless steel, and a high-modulus material obtained by using carbon fiber as a reinforcing material, i.e., carbon fiber reinforced plastic called CFRP. Japanese Patent Laid-Open (Kokai) No. 60 7873 discloses an iron type club head in which the impact face portion of a head body is constituted by an Ni-Ti alloy containing 50 to 60 wt. % of Ni with the balance of Ti, or by a thermoelastic type martensite transformation alloy in which part of Ni or Ti of an Ni-Ti alloy is substituted with at least one element selected from the group consisting of Fe, Co, Zr, V, Cu, and Al. In addition, Japanese Patent Laid-Open (Kokai) No. 60-7872 discloses a wood type club head, in which the impact face portion of a head body is constituted by a Cu thermoelastic type martensite transformation alloy containing at least one element selected from the group consisting of Zn, Al, Ni, Si, Sn, Mn, Ag, Mg, Sb, Ga, Ge, and In within the range in which a 8 brass structure can be obtained with the balance of Cu.
In such a golf club structure, since the impact face portion of a head body is made of a thermoelastic type martensite transformation alloy exhibiting thermoelastic martensite transformation within the temperature range of -120.degree. C. to +20.degree. C., super elastic behavior upon rebounding of a ball due to flexibility based on a stress-induced martensite caused upon impact can be utilized to increase the contact area of the head with the ball and prolong a contact time. Therefore, so-called "ball holding" is good. As a result, the directivity of the hit ball is stable, and the carry can be increased.
In the above-described club head, however, the impact face portion of a head body is simply constituted by thermoelastic type martensite transformation alloy exhibiting thermoelastic martensite transformation, and the head body has a solid structure while the impact face portion is backed up by another head material. In such a club head, even though the head body has a hollow structure, if the thermoelastic type martensite transformation alloy has a normal thickness of about 6 to 10 mm, super elastic behavior upon rebounding of a ball due to flexibility based on a stress-induced martensite caused upon impact cannot be efficiently utilized. Therefore, the effects of improving energy transmission with an increase in contact area of the head with a ball and prolonging a contact time cannot be fully realized.